Elongated items such as wiring bundles or optical fiber cables used for telephone, video or computer communication networks are often installed in protective ducts which may be buried underground, strung from support stanchions or positioned within building structures along with other utility and service lines. Such ducts may be, for example, extruded polymer tubes which provide substantially continuous protection to the elongated items from moisture, abrasion, impact and other environmental hazards.
Once the duct is in place, for example, underground or throughout a building structure, it is difficult to position additional cables within it, for example, to increase the capacity of the communication network or replace a failed cable. When the ducts are buried underground or positioned within the structure of a building, they are accessible only at isolated node points where the network is connected to components or splices are effected. The relative inaccessibility of the duct work often precludes any attempt to use it for additional cables. New ducts are laid or installed or the existing duct work is scrapped and replaced with new ducts having increased capacity.
The duct work through which the wiring bundles or optical fiber cables are installed may also comprise the heating and air conditioning ducts within a building. Such duct work provides a convenient means for supporting and distributing the communication lines throughout the building structure.
Placement of these communication lines within the duct work is done after the duct work is installed, either during building construction or in an established building in which the facilities are being updated or augmented. Installation of the lines within existing duct work is often a difficult task since the duct work typically does not follow a straight path, but winds its way throughout the building structure. Typically, the lines must be drawn through the duct work, sometimes under considerable tensile force.
Furthermore, items, such as the aforementioned communication lines, if installed within ventilation ducts, such as air conditioning ducts, must meet the fire safety requirements of the Plenum Rating Standard established by Underwriters Laboratories. The Plenum Rating Standard UL1995 establishes minimum requirements for both flame spreading and smoke development based upon test specifications, particularly the Surface Burning Characteristics of Building Materials and assemblies, CAN/ULC-S102, and the Standard Method of Tests For Surface Burning Characteristics of Building Materials, UL 723. According to the Plenum Rating Standard, material in a compartment handling conditioned air for circulation through a duct system shall have a flame spread rating of not more than 25 and a smoke developed rating of not more than 50 when tested according to the aforementioned specifications. By adhering to such codes, greater fire safety is achieved since the elongated items within the duct work will resist burning and smoking during a fire, and the duct work will not become a means for spreading fire and smoke throughout the building.
The insulation used with electrically conducting wire and the sheathing for optical fibers typically do not meet the requirements of the Plenum Rating Standard. This prevents positioning of such items within the air conditioning duct work of a building.
There is clearly a need for an apparatus and method for installing additional elongated items, such as optical fiber cables or wire bundles within in-situ ducts, which does not require access to the duct substantially along its length but will allow for relatively easy installation of additional elongated items with only access to terminal points of the duct. It is furthermore desirable that, at least for some applications, the protective sleeving meet or exceed the Plenum Rating Standard to afford greater protection to the elongated items from fire and allow them to be installed within the ventilation duct work of a building.